On the criteria for the initiation of motion in tidal inlets,deterministic and stochastic approaches     

Morteza Kolahdoozan  Hanifeh Imanian  Roger A. Falconer 《Coastal Engineering》2011

Details are given herein of the refinement and application of a three-dimensional layer integrated numerical model to predict morphological changes in tidal basins. The solution of governing differential equations, which consist of the conservation of mass and momentum for the hydrodynamics, the transport equation for the suspended sediment fluxes and the sediment mass conservation equation for the bed level changes are carried out by the use of Alternating Direction Implicit (ADI) Finite Difference Method (FDM). The model includes different criteria for the initiation of motion namely Shields (1936, Application of Similarity Principles and Turbulence Research to Bed load Movement, Hydrodynamics Laboratory, California Institute of Technology, Pub. No. 167), Kolahdoozan (1999, Numerical Modelling of Geomorphological Processes in Estuarine Waters, PhD Thesis, Department of Civil and Environmental Engineering, University of Bradford, Bradford, UK, 288) and Zanke (2003, On the Influence of Turbulence on the Initiation of Sediment Motion, International Journal of Sediment Research, 18(1), 17–31), to compare different aspects of flow conditions. As the flow is highly turbulent with the random nature of its components, many researchers have tried to express sediment transport processes by using stochastic approaches. In the current study both deterministic and stochastic methods are included in the numerical model to evaluate their accuracy and efficiency. To validate the numerical model results, laboratory measurements are used, with these being obtained from an earlier experimental program undertaken by the authors. Results of a short term bed level changes in a laboratory model harbor are included for the model verification purposes. Comparisons are undertaken using different criteria for the initiation of motion, with the results highlighting that the unsteadiness in the flow parameters included in the numerical model has a major effect on the bed level changes inside the harbor, in compare with the turbulence structure of the flow. The model is then applied to a real case study of the Humber Estuary, located in the UK, with comparisons being undertaken for different criteria for the initiation of motion, using both deterministic and stochastic approaches for the long term bed level predictions.  相似文献   

Measurement and modeling of bed shear stress under solitary waves   总被引：1，自引：0，他引：1  

Jaya Kumar Seelam  Paul A. Guard  Tom E. Baldock 《Coastal Engineering》2011

Direct measurements of bed shear stresses (using a shear cell apparatus) generated by non-breaking solitary waves are presented. The measurements were carried out over a smooth bed in laminar and transitional flow regimes (~ 10⁴ < R_e < ~ 10⁵). Measurements were carried out where the wave height to water depth (h/d) ratio varied between 0.12 and 0.68; maximum near bed velocity varied between 0.16 m/s and 0.51 m/s and the maximum total shear stress (sum of skin shear stress and Froude–Krylov force) varied between 0.386 Pa and 2.06 Pa. The total stress is important in determining the stability of submarine sediment and in sheet flow regimes. Analytical modeling was carried out to predict total and skin shear stresses using convolution integration methods forced with the free stream velocity and incorporating a range of eddy viscosity models. Wave friction factors were estimated from skin shear stress at different instances over the wave (viz., time of maximum positive total shear stress, maximum skin shear stress and at the time of maximum velocity) using both the maximum velocity and the instantaneous velocity at that phase of the wave cycle. Similarly, force coefficients obtained from total stress were estimated at time of maximum positive and negative total stress and at maximum velocity. Maximum positive total shear stress was approximately 1.5 times larger than minimum negative total stress. Modeled and measured positive bed shear stresses are well correlated using the best convolution model, but the model underestimates the data by about 4%. Friction factors are dependent on the choice of normalizing using the maximum velocity, as is conventional, or the instantaneous velocity. These differ because the stress is not in phase with the velocity in general. Friction factors are consistent with previous data for monochromatic waves, and vary inversely with the square-root of the Reynolds number. The total shear stress leads the free stream fluid velocity by approximately 50°, whereas the skin friction shear stress leads by about 30°, which is similar to that reported by earlier researchers.  相似文献   

中国南方下寒武统黑色岩系及其地质研究意义     

牛丙超 《云南地质》2013,(4):484-487

黑色岩系是C、N、P、S、O和一些重金属的循环链,既是一种矿产资源,又是环境因素的良好载体.以我国南方下寒武统为例,讨论黑色岩系的地质研究意义,提出黑色岩系的重点研究方向.  相似文献   

Transition from wavelets to ripples in a laboratory flume with a diverging channel   总被引：3，自引：1，他引：2  

William B. RAUEN  Roger A. FALCONER 《国际泥沙研究》2008,23(1):1-12

An experimental investigation on the initiation and development of bed forms on a bed of fine silica sand was conducted under alluvial flow conditions in a laboratory flume with a diverging channel. The main aims of the study were to assess： i） the steepness of bed forms in the transition stage of development; and ii） the threshold height of wavelets （ηt） that triggered the start of ripple development. Detailed bed profile measurements were carried out using an acoustic Doppler probe, traversed longitudinally over the sediment bed at various experimentation times. The bed form dimensions were extracted from such bed profile records and analysed for the wavelet, transition and equilibrium stages. It was found that the steepness of ripples in the transition and equilibrium stages were similar, confirming predictions of previous mathematical model simulations. A lognormal distribution fitted the wavelet length data. The wavelet threshold height was estimated as ηt ≈ 7 mm, or ηt≈ 80 in wall units. Such a height magnitude suggested that ripple development could be triggered by the wavelets reaching the outer flow zone of a turbulent boundary layer. The ηt value obtained corresponded generally to the intersection point between two predictive equations for bed form dimensions. A formulation was developed to predict ηt as a function of the sediment grain size, which was confirmed for the fine sand used in this study.  相似文献   

Numerical Simulation of Bed Separation Development and Grout Injecting into Separations   总被引：2，自引：0，他引：2  

Shou Gen Chen  Hua Guo 《Geotechnical and Geological Engineering》2008,26(4):375-385

In this paper, the Cosserat theory that has been incorporated into a three dimensional finite element code COSFLOW, is applied to analyze the development of bed separations in the layered overburden and grout injection into the bed separations. The mechanism of bed separation development during the longwall mining is investigated. A parametric study is carried out to investigate the effect of major factors including hard rock grade, panel height and panel weight on bed separation development. Based on the modeling, a conceptual model to describe the development process of bed separation is proposed. The effect of grout injecting into the bed separations on subsidence reduction is also studied and the conclusion agrees well with the common realization.  相似文献   

EFFECTS OF SEDIMENT GRADATION ON THE GEOMETRY OF RIVER DELTAS     

Chjeng-Lun SHIEH  Chih-Ming TSENG  and Shaohua Marko HSUProfessor  Department of Hydraulics  Ocean Engineering  Director  Disaster Prevention Research Center  National Cheng-Kung University  Tainan  Taiwan    China. Ph.D. Candidate  Department of H 《国际泥沙研究》2001,16(1)

l INTRODUCTlONIn this study, formation of alluvial deltas was treated as a river-dominated type of topograPhy process,caused simply by sediment deposition from a channel into a wide basin. The influences of waves, tides,and density differences related to coastal effects were excluded. There have been numerous experimentalstUdies on river delta problems. For examPle, Shieh et al. (1988, 1997) used coarse sediment asexperimental material and revealed the development and the geometric simil…  相似文献   

GRAVEL SLUICING IN ALPINE RUN-OF-RIVER HYDROPOWER PLANTS     

Helmut SCHEUERLEIN Institut flier Wasserbau  Univeristy of Innsbruck  Technikerstn . A- Innsbruck  Austria. 《国际泥沙研究》2001,16(2)

1 INTRODUCTIONNdsral rivers entering reservoirs carry also sediment, partly as bedload and patly in suspension. At theentrance of the reservoir flow velocity is considerably reduced and the capability of sediment transport isdrashcally fading. Bedload maerial is deposited totally at the reservoir entrance fondng a delta, material...in suspension is cAned further intO the reservoir ulh.. it is partly deposited and partly dischargedthrough the dam towards downstreaxn (depending on the trapp…  相似文献   

EXPERIMENTAL STUDY ON SALTATION OF SOLID GRAINS IN FLOWING WATER     

HU Chunhong  HUI Yujia  and XIA Zhenhuan 《国际泥沙研究》1992,(2)

This paper deals with the saltation of bed-load solid grains in flowing water. Experiments have been carried out by means of high-speed photographing and advanced data processing techniques while the analysis is made by combined method of mechani- cal and statistical theories. Experiments reveal that saltation is the main form of the bed-load transport under ordinary flow conditions. Taking successive saltation as the model of bed-load transport, systematic analysis has been made with regard to the forces acting on grains and the variation of their magnitudes along the saltation trajec- tories to obtain the kinematic and dynamic properties of these grains. The statistical analysis shows that the probability density functions of the relative height and length of saltation are in conformity with distribution, while the probability density functions of the relative velocities of saltation are in conformity with the Gaussian distribution.  相似文献   

SEDIMENT PROBLEMS AT DUJIANGYAN PROJECT     

Xu Muju 《国际泥沙研究》1990,(2)

1. THE GEOGRAPHICAL ENVIRONMENT AND HISTORICAL PERSPECTIVE OF THEPROJECTIn the western part of Sichuan Basin, between the Longmen Mountain in the west and theLongquan Mountain in the southeast, lies an alluvial plain of 6500 kmZ formed by the Minjiang Riversystem known as the Chengdu Plain. With its mild climate (average annual temperature 16' 4 C ),fertile soils, rich water resources, and the densely interconnected system of Minjiang and TuojiangRivers, Chengdu …  相似文献   

Bed changes at toe of inclined seawalls     

Mousa S. El-Bisy   《Ocean Engineering》2007,34(3-4):510-517

This study was carried out to investigate the scour phenomenon at the toe of seawalls and the different parameters that affected it. Experiments were achieved using different wave steepnesses, bed material grain sizes, wall positions and inclinations. Based on experimental results, the parametric plots of toe scour for smooth impermeable inclined seawalls were prepared. Also, this paper presents the bed changes prediction at seawalls toe using artificial neural networks on the basis of experimental data to widen the range of application. Suitability of using a neural network model was developed, and a model was validated. It is proposed that this model can be used in coastal engineering applications.  相似文献